This application claims the priority of German patent document 197 06 382.9, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for testing for proper connection of lambda sensors in an internal combustion engine with one or more cylinder groups, where the engine includes an engine control and a plurality of lambda sensors, with an independent exhaust line associated with each cylinder group, and the exhaust line has an exhaust catalytic converter and at least one lambda sensor with a lambda regulating unit connected thereto.
Internal combustion engines of this type are frequently used in motor vehicles, with the lambda sensors positioned upstream and/or downstream of the individual exhaust catalytic converters as required. It is known that a lambda regulating unit can be connected to a given lambda sensor, incorporating an integrator stage and usually a proportional stage, which is not of further interest in this connection. See for example the book by J. Kasedorf, "Steuerungselektronik an Motor und Kraftubertragung" [Control Electronics for Engine and Power Transmission], Vogel-Verlag, 1989, p. 164. In such internal combustion engines, gasoline engines with lambda stereo or quadro control for example, there is a risk of the lambda sensors being improperly connected so that a recognized lambda sensor signal is associated with the wrong cylinder group and the lambda regulating system can become unbalanced. The method of the type recited at the outset serves to detect such connection errors.
German patent document DE 44 23 344 A1 discloses a method of this kind in which the injection valves of one of two rows of cylinders are shut off for a period of time corresponding at least to the reaction or switching time of the lambda sensors. The lambda sensor signal of the lambda sensor associated with the row of cylinders that has been shut off is compared with a predetermined threshold value at the end of the shutoff period of the injection valves. If the connections of the lambda sensors have been made improperly, the lambda sensor signal will overshoot or undershoot the threshold value. An injection valve shutoff method of this kind constitutes a significant intervention in engine operation that makes this known method applicable only with the vehicle at rest, for safety reasons.
Methods for detecting improper operation of an individual lambda sensor in an internal combustion engine are known from German patent document DE 41 17 986 C2 and U.S. Pat. No. 5,212,947, in which the air/fuel ratio of an air/fuel mixture supplied to the engine is adjusted while maintaining an ignitable mixture. The signal from the lambda sensor is then investigated to determine whether it indicates a reaction associated with the change made in the air/fuel ratio, thus indicating a correct function of the lambda sensor. The change in the air/fuel ratio in these known methods is accomplished by a square-wave-shaped variation thereof and/or by alternating reversal of an air/fuel ratio correction factor by an amplitude that can be set in advance.
The object of the invention is to provide a method of the type referred to previously that permits testing for properly connected lambda sensors without significantly interfering with normal engine operation.
This and other objects and advantages are achieved by a first embodiment of the method according to the invention in which, by means of the engine control, the lambda-regulating unit of a given cylinder group (and hence the composition of the fuel/air mixture to be injected into the cylinder in question that is regulated by the lambda-regulating unit) is changed relative to the current state of regulation or its regulating function is suspended during a delay period while retaining the injection of an ignitable mixture at the beginning of a delay period that includes at least the reaction or switching time of the lambda sensors. The lambda regulation is influenced by adjusting or suspending the operation of an integrator stage of the lambda-regulating unit for a delay that can be set in advance. As a result, the fuel/air mixture supplied is influenced, i.e. enriched or leaned out, for the cylinder group in question, said enrichment or leaning out being so slight that it does not significantly interfere with normal engine operation yet, is sufficient to trigger a reaction in the lambda sensor or sensors connected with the particular cylinder group.
Following the elapse of a typical delay time for adjustment, the signals from the one or more lambda sensors intended for this particular cylinder group is checked to determine whether they show a reaction associated with the manipulation performed on the integrator stage in question. In the case of lambda sensors located in line upstream or downstream of an exhaust catalytic converter, when the sensors are properly connected, this reaction produces sensor signals that reflect a time shift in the manipulation performed; that is, first in the sensor located upstream of the catalytic converter and then in the sensor located downstream of the catalytic converter. If the anticipated reaction occurs, it can be concluded that the lambda sensors are properly connected to this cylinder group. If no such sensor signal reaction occurs, the lambda probes have been connected in reverse. The decision can be made on the basis of suitably specified characteristic curves or threshold values for the respective lambda sensor signals.
Because the resulting intervention in engine operation is only minor, the method can be performed while driving, for example simultaneously with other diagnoses performed when the vehicle is in operation, with typical diagnostic times on the order of 0.1 second to 180 seconds. This saves warming up the engine until the catalytic converter operating temperature is reached specifically to perform this test for correctly connected lambda sensors.
In a second embodiment of the invention, the integrator stages for two groups of cylinders are influenced simultaneously, one in the direction of richer engine operation and the other toward leaner engine operation. This permits increased diagnostic reliability.
A third embodiment is especially suitable for checking the correct connection of at least two lambda sensors connected in series within a cylinder group. This procedure is also especially suitable for cold starts, since exhaust oscillations, i.e. lambda fluctuations, can even be measured downstream of an exhaust catalytic converter that is still cold.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.